well, assuming you already know how to turn the tuning keys i.e. the knob things on the head of a guitar. for first time tuning, you should definately a tuner. most of the time they're pretty cheap and easy to use. only thing you have to really know is the names of each string, which are the notes that they're usually tuned to. going from the thickest string (6th string) to the thinnest (first string) the names of the strings:
E
A
D
G
B
e
(the little e is for the 1st string, and it is tuned an octave higher than the
6th)
oh and this may help you when you're starting out, but you should definately get to learning how to tune on your own.
this diagram basically explains how you do it by yourself. for example if you're trying to tune the A string(5th), you fret and play the 5th fret on the E string(6th), which is the A note, then you try to make the A string identical sounding to that note. you do this for all of them except when you're tuning the B string(2nd); instead of the 5th fret, it's the 4th. then you tune the e string(1st) to the 5th fret of the B. at this point in your playing, you should know a few things by then, such as chords/scales, so use those as a final check to see if you're in tune, i.e. if it sounds the way it's supposed to
so yea, that's about it, hope this helped
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